Step-by-step actuator for electromagnetic switches



Oct. '7, 1947. ,s, T. HUNT Em 2,428,569

ECTROMAGNETIG SWITCHES STEP-BY-STEP ACTUATOR FOR EL Filed Dec. 15, 1943 lns an 5 "m1.

a7 jagg- INVENTORS 72 Stanley 7."/-/u722 and 05760 5414: MT Gaffe; M 172/4 ATTORNEY WITNESSES:

Patented Oct. 7, 1947 STEP-BY-STEP ACTUATOR FOR ELECTRO- MAGNETIC SWITCHES Stanley T. Hunt and Frederick W. F. Goffe, Northampton, England, assignors to Express Lift Company, Ltd., London, England, a British company Application December 15, 1943, Serial No. 514,364 In Great Britain May 7, 1943 4 Claims.

Our invention relates to electromagnetically operated step-by-step switches and has for its object the provision of a switch having improved operating characteristics and increased reliability.

It is known that with electromagnetically operated step-by-stepswitches of the pawl and ratchet type, the rate of wear on the ratchet teeth and pawl presents problems of design, particularly on heavily loaded switches. We find that the major portion of wear occurson the teeth of the ratchet To this end, and in accordance with our invention we provide an electromagnetically operated pawl and ratchet driven switch in which a frictional clutch coupling and a displaceable direct drive coupling between a ratchet wheel and a cam shaft are arranged so that movement is not imparted to the cam shaft by the ratchet wheel until the ratchet wheel has completed a portion of its movement, and in which, when movement of the ratchet Wheel ceases, movement of the cam shaft continues until it. occupies its original position relative to the ratchet wheel.

According to another feature of our invention, overstepping is prevented by a portion of a ratchet wheel tooth moving against a face of the pawl when the pawl is in an operated position, andv in which during the movement of the ratchet wheel the operating tip of the pawl is in engagement only with the root of the tooth.

The above and other features of our invention will be more readily understood from the following description of a forward and reverse drive switch constructed according to one embodiment of our invention. Ihe description should be read in conjunction with the accompanying drawing, in which:

Figure 1 shows a front view, Fig. 2 a top View, and Fig. 3 a rear view of the switch;

Fig. 4 shows an extended view ofthe meanswhich couples the ratchet wheel to the driving shaft;

Fig. 5 shows a view of the section V-V in Fig. 4;

Fig. 6 shows an enlarged view of portions of the ratchet wheel, pawl and pawl backstop with the pawl in its operated position; and

Figs. 7, 8 and 9 show three differently shaped cams applicable in the illustrated switch instead of the cam shown in Fig. 3.

Referring to Figs. 1 through 4, a base plate B has an upwardly extending plate portion C provided with a circular opening D and firmly connected with an insulating body E by means of rivets orbolts F and G (Fig. 3). A bracket H (Fig. 2) is firmly secured to the portion C so as to extend across the opening D in some distance from the portion C. These interconnected elements form the rigid and stationary supporting structure for two identicaldrive mechanisms, one I for each direction of drive, which have a common magnetic frame l firmly secured to the base plate and an adjustable pole member 4 or 4 which is screwed into a threaded hole in the core 2 or 2' and secured in proper position by a nut 5 or 5. Each drive contains further an armature 1 or 1' pivoted on a kn fe edge 46 or 46 formed by the upturned ends of the frame I. is biased by a restoring spring 8 or 8'. Two armature backstops 2| and 2i are mounted on the plate C in order to limit the spring biased motion of the armature I and 1, respectively. A pawl bearing block a or 9' is fixed to one end of a flat spring It or H! whose opposite end is se-. cured to'the armature T or 1 by a screw II or H. A pawl arm [2 or (2' is pivotally linked at 35 or 35 to the bearing block 9 0r 9. Each of the pawl arms [2 and [2' has a U-shaped cross section as is best apparent from Fig. 4. A spring l3 links the two arms 12 and I2 together and biases them towards a ratchet wheel M. A pawl,

15 or [5' is mounted between the two parallel side walls of each pawl 12 or 12. A U-shaped backstop It or IE is secured to the lateral portion I! or H of the bracket member H. The portions I! or H are provided with adjusting screws ['8 and I8, respectively, each carrying a locking nut I!) or [9.

A standard K of insulating material is firmly mounted on the base plate B (Fig. 1) and carries two sets of electrical contacts denoted by 20 and 26'. These contacts are to be provided only if a self-interrupter circuit is required for the electromagnet and are then operated by the armatures l and 1, respectively.

The ratchet wheel M has two shoulders 36 (Fig.

4.) against which the two parallel sides of the Each armature pawl arm [2 or l2 rest when in their inoperative positions. The ratchet wheel 14 is mounted on a cam shaft 22 and rotatable about this shaft within limits as described later in this specification. The longer arm of each U-shaped pawl backstop l6 and it is forced away from the shorter arm by means of the adjusting screw H! or I8 so that an slack in the adjusting screw thread is taken up. Consequently, the back of each pawl I2 and I2 slides always against a rigid backstop at the end of the operative pawl motion.

Referring to Figs. 4 and 5, the ratchet wheel I4 is movable around the cam shaft 22 within the limits imposed by the pins 24 and 25 fixed in the raised portion 26 of the cam shaft. The pins are of smaller diameter than the holes 31 and 38 in the ratchet wheel. The faces of the ratchet wheel friction disc 35 under the influence of the helical spring 23 make contact with the ratchet wheel [4 and the sleeve member 2'! screwed on the shaft 22. The amount of friction produced by the friction disc 30 upon the sleeve member 21 and the ratchet wheel I4 can be adjusted by screwing the s1eeVe member towards or away from the portion 26 of the cam shaft. The position of the sleeve member on the cam shaft is then secured by passing the pin 33 through one of a plurality of holes in the sleeve member and through a hole in the cam shaft.

The amount of friction caused by disc 28 between the bearing 29 and the sleeve member 21 can be adjusted by means of the spring 32, the ends of which are slidable on the bracket H within the limits imposed by the engagement of the elongated holes and 52 with the pins 53 and 54 of bracket H (Fig, 4). The tension of the spring is adjusted by means of a nut 34.

According to Fig. 3, an insulated cam 39 is held in a slot of a cam fixing plate 50 which is slidable along the hexagonal cam shaft 22 and is clamped in position by a screw 42 and a nut 43. The cam selectively operates the electrical contacts 40 and 4| corresponding to the number of impulses received by the two electromagnets. The length of the operating surface of the cam corresponds to the number of steps moved by the cam shaft during which the electrical contacts are required to remain operated.

It will be understood that the hexagonal portion of the cam shaft 22 may be provided with any number of cam members in accordance with the desired number of contact sets to be operated simultaneously by the switching device. Since all of these sets are similar in design and function, only one set is illustrated in Figs. 2 and 3 of the drawing.

The cams shown in Figs. 7, 8 and 9 are used when the electrical contacts are required to be operated in one position of the ratchet wheel. In Fig. '7, l1 denotes the fixing plate and 19 the insulated cam. In Figs, 8 and 9, 81 and 91 are fixing plates and 89, 99 the operating cams, respectively. In Fig. 8 it Will be seen that the hexagonal hole for shaft '12 is pierced in a different position from that in Fig. 3, thereby producing a 30 displacement of the cam on the cam shaft. In Fig. 3, the cam itself is displaced by 15. With a ratchet wheel having 24 teeth, it is, therefore, only necessary to provide two patterns of cam fixing plate and two patterns of cam in order to operate the electrical contacts in any one of the 24 positions of the cam shaft.

The operation of the switch will now be described in detail with particular reference to one of the two driving mechanisms. The other mechanism operates in the same manner except that it drives the ratchet wheel and cam shaft in the opposite direction of rotation.

When the coil 3 is energized, the armature l operates the electric contacts 20, and the tip 44 of the pawl l5 moves against the root 48 of the ratchet wheel tooth 45, so that the ratchet wheel I 4 moves one step. The tip of the pawl and the root of the ratchet wheel tooth are both slightly rounded so that the pawl tip moves smoothly in the root of the tooth. The pawl rotates the ratchet wheel until the pawl becomes wedged between the face 49 of the ratchet wheel tooth and the pawl backstop It as shown in Fig. 6. The portion 41 of the pawl which moves against the pawl backstop is shaped so that the thrust from the tooth face 49 is directly in line with the axis of the screw 18. The pawl backstop I6 is constructed in the form of a U-shaped spring, the shorter limb of which is fixed to the portion I! of the switch framework and the longer limb of which is tensioned away from the ratchet wheel. The longer limb of the U-shaped backstop is moved towards the ratchet wheel by turning the adjusting screw I8 into the threaded hole in the framework I! until it occupies its correct position. The adjusting screw is then secured in position by means of the nut I 9 which is placed on the outside of the framework so that, when tightened, it does not reverse the direction of thrust produced by the longer limb of the U- shaped backstop. Such a reversal of thrust would substantially alter the position of the longer arm of the backstop with respect to the framework I! and consequently in relation to the axis of the ratchet wheel.

When the pawl is wedged between the ratchet wheel tooth face 49 and the pawl backstop, the tooth face is substantially parallel to the longer limb of the pawl backstop so that when the armature releases, the pawl is able to slide clear of the ratchet wheel tooth without exerting a thrust which might displace the ratchet wheel. When the pawl becomes clear of the tooth face 49, the two arms of the pawl arm I2 are moved against the shoulders 38 of the ratchet wheel by the spring l3.

When the ratchet wheel is moved by the pawl, the first portion of its movement does not produce any substantial movement of the cam shaft 22. The ratchet wheel is frictionally connected to the cam shaft and by this means the initial shock of the pawl striking against the tooth of the ratchet wheel is considerably less than would be the case if the pawl was required to move the relatively heavy cam shaft and cam asssemblies, consequently one of the most serious causes of wear to the ratchet wheel and pawl is substantially re duced.

When the ratchet wheel has completed a portion of its movement, one side of each of the holes 3'! and 38 move against the pins 24 and 25 respectively, so that the ratchet wheel now rotates the cam shaft through a direct coupling.

When the ratchet wheel has completed its movement, the cam shaft continues to move due to the momentum imparted to it by the ratchet wheel, until the pins 24 and 25 move against the opposite sides of the holes 31 and 38 in the ratchet wheel. By this means, the friction connection between the ratchet wheel and the cam shaft substantially dissipates the momentum of the cam shaft so that the force exerted by the pins against the holes in the ratchet wheel is relatively small, consequently the ratchet wheel face 49 exerts only a small force against the pawl with the result that the risk of damage to the tip of the pawl and to the root of the ratchet wheel tooth is very considerably reduced.

It will be appreciated that if the pawl arm 12 is rigidly connected to the armature, slight variations in manufacture or adjustment may affect the proper wedging of the pawl between the face 49 of the ratchet wheel tooth and the pawl backstop if the magnetic gap between the armature and the face of the iron core is too narrow, whereas if the magnetic gap is too wide, undue wear of the tip of the pawl and the root of the ratchet wheel teeth can result. In the former case the ratchet wheel is inaccurately positioned and in the latter case the release time of the armature is altered.

To overcome the above difliculties, the pawl arms I2 and I2 are connected to the appertaining armatures by means of the flat spring I0 or It, and the inner iron core 4 or 4' is positioned so that when the armature moves against the face of the core, the flat spring is slightly raised from the armature.

The inner iron core also provides a means for adjusting the release time of the armature to a predetermined period of time.

Being aware of the fact that the above described invention may be modified Without departing from its objectives and essential features, we Wish this specification to be understood as illustrative and not in a limiting sense.

We claim as our invention:

1. A ratchet mechanism for an electric switch, comprising a rotatable member for actuating the switch, an electromagnetic step-by-step drive, frictional coupling means and lost-motion direct coupling means both disposed between said drive and said member so that movement is imparted to said member by said direct coupling means only after said drive has passed through an initial portion of its driving motion and said movement continues'to a limited extent after cessation of said driving motion, said frictional coupling means being arranged so as to be efiective to yield during the periods of said initial portion of movement and the periods of said continued movement.

2. A ratchet mechanism for an electric switch, comprising a shaft for actuating the switch, an electromagnetically operated ratchet drive for imparting step-by-step rotation to said shaft, a frictional coupling and a direct lost motion coupling both disposed between said drive and said shaft so that movement is imparted to said shaft by said direct coupling only after said drive has passed through an initial portion of its driving motion and said movement continues to a limited extent after cessation of said driving motion, said frictional coupling being arranged so as to yield during the periods of said initial portion of movement and the periods of said continued movement.

3. A step-by-step drive for electric switches comprising, in combination, a driven member, a shaft for driving said member, a ratchet wheel revolvably mounted on said shaft and having a hole spaced from said shaft, a sleeve member fixed to said shaft, a friction disc disposed between said ratchet wheel and sleeve member to form a frictional driving connection, a pin fixed to said shaft and engaging the wall of said hole, said pin having a smaller cross section than said hole to form a lost motion coupling, and an electromagnetically operated pawl assembly for driving said ratchet wheel.

4. A ratchet mechanism, comprising a ratchet wheel, an elongated ratchet member eng geable with said wheel, said member extending substantially in a tangential direction relative to said wheel and being movable substantially in said direction for imparting driving movement to said wheel, a stationary back-stop of substantially U-shaped configuration having its two limbs extending substantially in parallel to said direction, one of said limbs being engageable by said pawl member so as to form a guide for said member during the driving movement of said member, and an adjusting screw extending across said limbs for adjusting said one limb toward and away from said wheel.

STANLEY T. HUNT. FREDERICK W. F. GOFFE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,028,571 Smulski Jan. 21, 1936 2,377,733 Waller June 5, 1945 543,597 Dixon July 30, 1895 1,830,553 Love et a1 Nov, 3, 1931 2,135,204 Staley et a1. Nov. 1, 1938 284,755 Pidgin et a1. Sept. 11, 1883 703,263 Hudson June 24, 1902 732,730 Gemill July 7, 1903 2,318,359 Bellows May 4, 1943 2,177,088 Albertoli Oct. 24, 1939 378,436 Delany Feb. 28, 1888 1,012,079 Howe Dec. 19, 1911 1,720,189 Jackson July 9, 1929 1,979.824 Christensen et al. Nov. 6, 1934 1,090,301 Hawkins Mar. 17, 1914 2,235,038 Pearce et a1 Mar, 18, 1941 1,505.480 Manville Aug. 19, 1924 1,557,525 Hanson Oct. 13, 1925 2,243,738 Mather May 27, 1941 

